Batteries prepared by spinning

ABSTRACT

Methods of forming a lithium-ion battery on a vehicle component by spinning and vehicle components with a batteries formed thereon are disclosed. The spinning may include electrospinning. A first electrode layer may be spun, followed by a first separator layer, a second electrode layer, and a second separator layer. Each layer may be spun directly onto the previously spun layer to provide a battery that does not include metal current collectors. The anode and/or cathode layers may include polyacrylonitrile (PAN) fibers. To render the anode and cathode layers conductive, they may be carbonized using a heat source (e.g., a laser). The disclosed method may allow for the formation of batteries directly onto a vehicle component, such as a body panel, thereby using otherwise empty space to increase the battery capacity of the vehicle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/445,263 filed Jul. 29, 2014, the disclosure of which is herebyincorporated in its entirety by reference herein.

TECHNICAL FIELD

The present disclosure relates to spun batteries and methods ofpreparing the same.

BACKGROUND

Enhancement of battery performance is an important issue in theadvancement of portable electronics, power grid regulation, andelectrified vehicles. Rechargeable or secondary batteries generallyinclude positive and negative electrodes, a separator, and anelectrolyte. Current collectors are attached to each electrode in orderto extract current from the battery. Rechargeable batteries, such aslithium-ion batteries, have not yet attained the necessaryspecifications in energy density and rate capability that are needed tomake long-range electric vehicles (EVs) a viable option for manyconsumers. The relatively limited porosity of the electrodes, lowspecific capacities of cathode materials, and added weight from batterycomponents are significant factors in these short comings.

SUMMARY

In at least one embodiment, a lithium-ion battery is provided. Thebattery may include a first anode layer including a conductive bulkfiber and an anode active material, a first non-conductive, porous layercontacting the first anode layer, a first cathode layer including aconductive bulk fiber and a cathode active material contacting the firstnon-conductive, porous layer, and a second non-conductive, porous layercontacting the first cathode layer.

At least a portion of the anode active material may be embedded in theconductive bulk fiber of the anode layer and at least a portion of thecathode active material may be embedded in the conductive bulk fiber ofthe cathode layer. The anode active material may include siliconnanoparticles and the cathode active material may include sulfur, suchas nanoparticles of elemental sulfur or Li₂S. Each of the first anodeand cathode layers may include a body and a collector tab extending fromthe body, the collector tab including a conductive bulk fiber. Theconductive bulk fiber of the first anode and cathode layers may be acarbonized polymer. The first and second non-conductive, porous layersmay be first and second separator layers.

The battery may further comprise a second anode layer including aconductive bulk fiber and an anode active material contacting the secondseparator layer, a third separator layer contacting the second anodelayer, and a second cathode layer including a conductive bulk fiber anda cathode active material contacting the third separator layer.

In at least one embodiment, a lithium-ion battery is provided comprisinga plurality of anode layers, each including a conductive bulk fiber andan anode active material, a plurality of cathode layers, each includinga conductive bulk fiber and a cathode active material, and a pluralityof non-conductive separator layers, each separating one of the pluralityof anode layers from one of the plurality of cathode layers.

The anode active material may include silicon and at least a portion ofthe anode active material may be embedded in the conductive bulk fiberof each anode layer. The cathode active material may include sulfur andat least a portion of the cathode active material may be embedded in theconductive bulk fiber of each cathode layer. In one embodiment, no metalcurrent collectors are in contact with the plurality of anode layers orthe plurality of cathode layers. The plurality of anode layers and theplurality of cathode layers may have a porosity of 40% to 80%. Theplurality of separator layers may each have a thickness of 1 to 12 μm.

In at least one embodiment, a method for forming a battery is providedcomprising (a) spinning a first anode layer; (b) spinning a firstseparator layer onto the first anode layer; (c) spinning a first cathodelayer onto the first separator layer; and (d) spinning a secondseparator layer onto the first cathode layer.

The method may further include the steps of carbonizing the first anodelayer prior to step (b) and carbonizing the first cathode layer prior tostep (d). In one embodiment, the carbonizing steps are performed using alaser. The spinning in steps (a)-(d) may be performed usingelectrospinning. Step (a) may include spinning a polyacrylonitrile (PAN)fiber and an anode active material and step (c) may include spinning aPAN fiber and a cathode active material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating the electrospinning process;

FIGS. 2A-2C are mask patterns for a cathode, separator, and anode,respectively, according to an embodiment;

FIG. 3 is a schematic view of an electrospinning process for preparingan electrospun battery, according to an embodiment;

FIG. 4 is a method of forming a rechargeable battery by electrospinning,according to an embodiment; and

FIG. 5 is a schematic view of an electrospun battery, according to anembodiment.

DETAILED DESCRIPTION

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention that may be embodied in variousand alternative forms. The figures are not necessarily to scale; somefeatures may be exaggerated or minimized to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting, but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention.

A conventional lithium-ion battery (LIB) generally includes a negativeelectrode (anode), a positive electrode (cathode), a separator, anelectrolyte disposed within the electrodes and separator, and a currentcollector contacting each of the anode and cathode. The currentcollector is generally formed of a sheet of copper or aluminum. A commonmethod of forming LIBs is to cast the anode and cathode materials ontotheir respective current collectors and then stack them with a separatorin between the anode and cathode materials. The anode and cathodegenerally include an active material and a binder. The active materialfor the anode is often a form of carbon, for example, graphite, whilethe active material for the cathode is often a lithium metal oxide. Thebinder may be aqueous or non-aqueous, such as carboxymethyl cellulose(CMC) or polyvinylidene fluoride (PVDF), respectively. Separators arecommonly made of a polyolefin, such as polyethylene or polypropylene.The electrolyte generally includes a lithium salt, such as LiPF₆, and anorganic solvent, such as ethylene carbonate (EC), dimethyl carbonate(DMC), diethyl carbonate (DEC), or mixtures thereof.

A number of high capacity materials, such as silicon (Si) and sulfur(S), may potentially increase the capacities of LIBs if incorporatedinto the anode and/or cathode. However, these materials may suffer fromdegradation and dissolution issues that prohibit their use in batterieshaving the standard architecture. For example, when sulfur is used inconventional LIBs, the sulfur may dissolve into and/or react with theliquid electrolyte and may form polysulfides (e.g., Li₂S₈). Thedissolution and/or reaction of the sulfur may therefore reduce theactivity of the electrode. In addition, once the sulfur is liberatedfrom, e.g., the cathode, it may migrate back and forth between theelectrodes. This shuttle effect may reduce the activity of theelectrodes and may lead to an ionic short in the battery. Silicon alsopresents difficulties when used in conventional LIBs. For example, whenSi alloys with lithium, its structure swells from a dense crystallinestructure to a larger, less dense structure. This large volume changecan lead to cracking in the electrodes over time, as the active materialswells and shrinks in cycles. The repeated volume changes and crackingcan lead to increased solid-electrolyte interphase (SEI) formation,particularly at the anode. In addition, the pulverized structure maycause the active material to lose contact with the metal currentcollector, reducing its activity.

It has been discovered that spinning (e.g., electrospinning) ofelectrode materials may provide the ability to encapsulate these highcapacity materials (e.g., S and Si) and thereby eliminate or mitigatesome of these issues. For example, when the active material in thecathode includes elemental sulfur or lithium sulfide particles (e.g.,Li₂S) and/or the active material in the anode includes siliconparticles, at least some of the particles may become embedded in theelectrospun fibers. The embedded particles may therefore have lessdirect interaction with the electrolyte. As a result, the dissolutionand/or formation of polysulfides may be mitigated or eliminated forsulfur-containing active materials. Rather than the sulfur reacting withthe lithium and potentially being dissolved into the electrolyte, thesulfur stays within the fiber and the lithium ions may diffuse throughthe fiber. Embedded silicon particles also are retained within thefibers, which may be conductive (discussed in more detail, below).Accordingly, the embedded particles may stay in contact with theconductive fibers in the swollen state, thereby retaining theiractivity. In addition, the encapsulation of the silicon particles shiftsthe interface with the electrolyte to the fibers instead of the silicon,which may reduce SEI formation.

It has also been found that spinning of electrode materials may providea massively interconnected porous network in the electrodes. However,spinning the electrodes may still require the use of a conventionalseparator, because the high temperature carbonization step needed tomake the electrodes conductive would also do the same to the separatorif the carbonization process was performed on a complete stack (e.g.,anode-separator-cathode).

Accordingly, with respect to FIGS. 1 to 5, a method of preparing a fullyelectrospun lithium ion battery (LIB) and a LIB prepared therefrom aredisclosed. The general process of electrospinning is known in the artand will not be described in great detail. In brief, electrospinningincludes applying a high voltage to a droplet of polymer solution ormelt, thereby inducing a strong charging effect on the fluid. At acertain charge level, electrostatic repulsion overcomes the surfacetension of the liquid and the droplet is stretched until a stream ofliquid is ejected from the droplet. The point of ejection is known as aTaylor cone. Molecular cohesion causes the stream to stay together, suchthat a charged liquid jet is formed. The liquid jet begins to solidifyin the air, at which point the charge in the liquid migrates to thesurface of the forming fiber. Small bends in the fiber lead to awhipping process caused by electrostatic repulsion. The whipping processelongates and narrows the fibers, generally resulting in a uniform fiberdiameter of 0.05 to 100's of micrometers (μm).

FIG. 1 is a schematic generally describing the electrospinning processand equipment. The electrospinning system 10 generally includes a powersupply 12, which may be a high voltage DC power supply (e.g., 5 to 50kV), a spinneret 14, a syringe 16 and a collector 18. The spinneret 14may be a hypodermic syringe needle or other narrow, hollow tubestructure. The spinneret 14 may be directly attached to the syringe 16or may be connected by a tube or hose 20. The spinneret 14 may bysupported by a stand 22, which may be configured to hold the spinneret14 at a certain position relative to the collector 18 (e.g., height,horizontal distance, angle). The spinneret 14 or the stand 22 may beelectrically connected to a positive terminal 24 of the power supply 12by a wire 26 and the collector 18 may be electrically connected to anegative terminal 28 of the power supply 12 by a wire 30. Alternatively,the collector 18 may be grounded.

During the electrospinning process, a polymer solution, sol-gel,particulate suspension, or melt may be loaded into the syringe 16, whichmay then be actuated by a pump 32 to force the polymer liquid 34 intoand through the spinneret 14, generally at a constant rate.Alternatively, the polymer liquid 34 may be fed to the spinneret from atank under constant pressure. The liquid is charged at the spinneret 14and forms a jet 36, as described above. As the jet 36 solidifies, itwhips into a fiber 38 and is collected on the collector 18. A variety offactors or parameters can affect the size and properties of theresulting fibers 38, including the molecular weight and type of thepolymer, solution concentration, the liquid properties (e.g., viscosity,conductivity, and surface tension), the electric potential and flowrate, the distance between the spinneret 14 and the collector 18,ambient conditions (e.g., temperature and humidity), the motion and/orsize of the collector 18, and the gauge of the needle or tube in thespinneret 14.

With reference to FIGS. 2-5, an electrospun battery and a method offorming an electrospun battery are disclosed. With reference to FIGS.2A-2C, masks are illustrated for patterning the components of a battery.FIG. 2A shows an embodiment of a cathode mask 50, which may have a bodyportion 52 for forming the electrode field and a tab portion 54 forforming a collector tab allowing connection to an external circuit. FIG.2B shows an embodiment of a separator mask 60, which may have a bodyportion 62. The separator mask 60 does not require a tab portion, sincethere is no connection to an external circuit from the separator. FIG.2C shows an embodiment of an anode mask 70, which have a body portion 72for forming the electrode field and a tab portion 74 for forming acollector tab allowing connection to an external circuit. While theelectrode masks are shown having a single collector tab portion, two ormore tab portions may be formed by the masks. The masks 50, 60, 70 maybe configured to form components having generally rectangular bodyportions, however, the masks may be configured to form any suitableshape.

With reference to FIG. 3, a schematic of an electrospinning system 80 isshown, which is a simplified diagram of FIG. 1. As shown, the system 80may include a spinneret 82 that may receive a liquid material from asource, such as a cathode material 84, separator material 86, or anodematerial 88. The source materials may be fed to a common syringe or pump90 that may select which source material to provide to the spinneret 82.The spinneret 82 may then direct a jet 92 of material towards acollector 96, forming a fiber 94 as the liquid solidifies on its way tothe collector 96. As a result, an electrospun component 98 is formed onthe collector 96. The fiber diameter may vary depending on theelectrospinning parameters. For example, the fibers may have a diameterof 50 nm to 50 μm.

A heating source 100 is provided, which may be a laser. The laser may bea pulsed laser, for example a Nd:YAG pulsed laser. The laser may beconfigured to raster over a surface of the electrospun component 98 inorder to heat the surface. In one embodiment, the heat generated by thelaser is used to carbonize the electrospun component 98 (e.g., cathodeor anode material) in order to make it electrically conductive (or moreelectrically conductive). Other heating sources may be used instead of,or in addition to, a laser. The heating source may be any device capableof heating localized regions of the electrospun component 98 that iscollected on the collector 96. In addition to heating localized areas ofthe component, the heating source may also be configured to heat apredetermined thickness of the component. For example, if a component 98has a thickness of 10 μm, the heating source 100 may be configured toonly heat a region to a depth of 10 μm, such that any material stackedbehind the component 98 is not significantly heated or is heated to asignificantly lower temperature.

Again with reference to FIG. 3, the cathode material 84, separatormaterial 86, and the anode material 88 may be any suitable materials toform a rechargeable battery, such as a LIB. In at least one embodiment,the cathode material 84 and/or the anode material 88 may include highcapacity materials, such as silicon, sulfur, or high capacity NMC. Forexample, silicon may have a specific capacity of up to 3,579 mAh/g andsulfur may have a specific capacity of up to 1,166 mAh/g. Thesematerials may provide increased capacity to LIBs, but suffer fromdegradation and dissolution issues when used in conventional batteryarchitectures, as described above. In at least one embodiment, thecathode material 84 includes a base polymer and a solvent capable ofdissolving the base polymer. In one embodiment, the base polymer ispolyacrylonitrile (PAN), a PAN co-polymer, or a PAN-derivative. Asuitable solvent for PAN may include dimethylformamide (DMF).

In addition to PAN, other base materials that can be heat treated toform stable, carbonized fibers without melting may be used. In someembodiments, the cathode material 84 may include a base polymer mixedwith an active material. The active material may include elementalsulfur and/or sulfur-containing compositions, such as lithium sulfide(Li₂S). However, other cathode active materials may be used, such aslithium nickel cobalt aluminum oxide (NCA), lithium nickel manganesecobalt oxide (NMC), lithium manganese spinel oxide (Mn spinel or LMO),and lithium iron phosphate (LFP) and its derivatives lithium mixed metalphosphate (LFMP). In addition, mixtures of any of two or more of thesematerials may be used, for example a mixture of NMC and LMO. The cathodeactive material may have a specific capacity of up to or greater than1,166 mAh/g. For example, the active material may have a specificcapacity of 500 to 1,166 mAh/g, 700 to 1,166 mAh/g, or 900 to 1,166mAh/g.

In at least one embodiment, the active material is present in the formof nanoparticles. Upon electrospinning of the cathode material 84, atleast some of the nanoparticles may become embedded within the basepolymer fibers. For example, a cathode component may be formed of PANfibers having S or Li₂S nanoparticles embedded therein. If non-lithiumcontaining materials, such as elemental sulfur, are used in the cathodematerial 84, the anode material 88 (discussed further, below) may belithiated prior to being electrospun, such that the battery may befabricated in a charged state.

In at least one embodiment, the separator material 86 includes a basepolymer and a solvent capable of dissolving the base polymer. Suitablebase polymers for the separator may include polyolefins, such aspolyethylene or polypropylene, or other polymers includingpolyvinylidene fluoride (PVDF). The separator material 86 may alsoinclude additives to improve is properties and performance. Examples ofadditives may include barium titanate (BaTiO₃) and/or alumina (Al₂O₃) toimprove thermal and mechanical properties.

In at least one embodiment, the anode material 88 includes a basepolymer and a solvent capable of dissolving the base polymer. In oneembodiment, the base polymer is polyacrylonitrile (PAN), a PANco-polymer, or a PAN-derivative. However, other base materials that canbe heat treated to form stable, carbonized fibers without melting may beused. Suitable solvents for PAN are discussed above with reference tothe cathode material 84. In some embodiments, the anode material 88 mayinclude a base polymer mixed with an active material. The activematerial may include, for example, silicon or silicon-containingcompounds. However, other anode active materials may be used, such asgraphite (natural, artificial, or surface-modified natural), hardcarbon, soft carbon, and lithium titanate oxide (LTO). The anode activematerial may have a specific capacity of up to or greater than 3,579mAh/g. For example, the active material may have a specific capacity of1,500 to 3,579 mAh/g, 2,000 to 3,579 mAh/g, 2,500 to 3,579 mAh/g, or3,000 to 3,579 mAh/g. In at least one embodiment, the active material ispresent in the form of nanoparticles. Upon electrospinning of the anodematerial 88, at least some of the nanoparticles may become embeddedwithin the base polymer fibers. For example, an anode component may beformed of PAN fibers having silicon nanoparticles embedded therein.

With reference to FIG. 4, a method 200 of forming an electrospun batteryis provided, according to an embodiment. The masks described in FIG. 2and the system described in FIG. 3 may be used to carry out the method200. In step 202, an anode material is electrospun onto a conductivecollector to form a first anode layer. A mask may be used to pattern theanode material into a body portion and a collector tab, such asdescribed with reference to FIG. 2C. While a single collector tab isshown, multiple collector tabs may be formed. In addition to masks,other methods may also be used to form the anode shape. One example mayinclude moving the electrospinning spinneret/nozzle in a predeterminedpattern, similar to CNC milling or 3-D printing. Another example mayinclude the use of an external electric field to direct the patterningof the fiber, similar to the directing of an electron beam in TVs havingcathode ray tubes. Furthermore, it may be possible to electrospin alarger than needed area and then cut or trim the layer into the desiredanode shape.

In step 204, the polymer in the anode layer is carbonized (e.g.,converted into substantially all carbon) using a heat source. The heatsource may be a laser or a pulsed laser, and it may be rastered over theanode layer surface to heat and carbonize the anode layer. Thecarbonizing step 204 may be a single step or may be split into two ormore steps. The structure of PAN fibers may be stabilized by a heattreatment of about 250-300° C., for example, 280° C. PAN fibers arecarbonized by a heat treatment of about 700-1200° C., for example, 900°C. The carbonization process may convert the polymer fiberssubstantially into carbon. Some residual elements may remain after thecarbonization process, such as nitrogen, however, the fibers aregenerally converted into amorphous carbon having a similar structure tothe original base polymer fibers. As a result of the other elementsbeing removed, such as hydrogen, the fibers may shrink slightly. PANfibers may further be graphitized by a heat treatment of at least about1400° C., converting the carbon fibers into graphitic carbon.

Accordingly, a single-step carbonization process may be performed byheating (e.g., by laser) the fibers directly to a carbonization orgraphitization temperature (e.g., about 900° C. or 1400° C. for PANfibers). Alternatively, a two-step carbonization process may beperformed by first heating the fibers to a stabilizing temperature(e.g., 280° C. for PAN fibers) and then separately heating the fibers toa carbonization or graphitization temperature. While the one-stepprocess may be faster and more efficient, the two-step process mayresult in a more stable structure for the fibers. The one-step processand at least the second step of the two-step process may be performed inan inert environment (e.g., argon or nitrogen) in order to preventoxidation/combustion. The stabilizing treatment of the two-step processmay also be done in an inert environment, however, it may also be donein air. Instead of an inert environment, it may also be suitable to usea heavy gas that displaces the ambient air to avoid oxidation.

In step 206, a separator material is electrospun onto the first anodelayer to form a first separator layer. In at least one embodiment, theseparator material is electrospun directly onto the first anode layer,with no intervening material. A mask may be used to pattern theseparator material into a body portion, such as described with referenceto FIG. 2B. As described above, however, other methods may be used toshape the separator layer. Unlike the anode layer, the separator is nottreated with a heat source to carbonize it; therefore, it retains itselectronic insulating properties.

In step 208, a cathode material is electrospun onto the first separatorlayer to form a first cathode layer. In at least one embodiment, thecathode material is electrospun directly onto the first separator layer,with no intervening material. A mask may be used to pattern the cathodematerial into a body portion and a collector tab, such as described withreference to FIG. 2A. While a single collector tab is shown, multiplecollector tabs may be formed. As described above, other methods may alsobe used to shape the cathode layer. In step 210, the polymer in thecathode layer is carbonized as described above with respect to the anodelayer. In order to avoid carbonizing the separator layer underlying thecathode layer, the laser or other heat source may be configured to onlyheat the cathode layer and not the underlying separator layer. Inembodiments where a laser is used as the heat source, the depth profileof the laser may be defined by controlling numerous parameters, such asthe total energy of the laser, the wattage, the wavelength, the spotsize, the raster speed, the pulse length, etc. It may be acceptable forsome heat to reach the underlying layer, as long as it remainssubstantially uncarbonized and retains sufficient porosity to allowlithium ion movement in the electrolyte.

Following step 210, a separator material (e.g., the separator materialof step 206) is electrospun onto the first cathode layer to form asecond separator layer in step 212. In at least one embodiment, theseparator material is electrospun directly onto the first cathode layer,with no intervening material (e.g., no current collector). Theelectrospinning of step 212 may be substantially similar to theelectrospinning of step 206, other than the underlying material (e.g.,first cathode layer instead of first anode layer). However, if adifferent thickness, different separator material, or other differentproperty is desired for the second separator layer, then theelectrospinning parameters may be adjusted for step 212. Similar to step206, no carbonization treatment is applied to the second separatorlayer.

In step 214, an anode material (e.g., the anode material of step 202) iselectrospun onto the second separator layer to form a second anodelayer. In at least one embodiment, the anode material is electrospundirectly onto the second separator layer. The electrospinning of step214 may be substantially similar to the electrospinning of step 202,other than the underlying material (e.g., second separator layer insteadof the collector). However, if a different thickness, different anodematerial, or other different property is desired for the second anodelayer, then the electrospinning parameters may be adjusted for step 214(the same applies for any additional cathode layers). Similar to step204, the polymer in the second anode layer may be carbonized using aheat source in step 216. The electrospinning of the anode, separator,and cathode layers in the steps above may be adjusted by alteringelectrospinning parameters such as potential, distance, needle size,temperature, solution concentration, polymer type, polymer molecularweight, target type (e.g., flat plate, rotating cylinder, etc.), orothers.

The stacking of separator, cathode, and anode layers may be continuedafter step 216 for a plurality of cycles to form multiple stacks oflayers. Each layer may be spun directly onto the preceding layer,without other intervening layers (e.g., current collectors). Each anodeand cathode layer may be carbonized by a heat source, such as a laser,while the separator layers may be left uncarbonized so that they retaintheir electronic insulating properties. While FIG. 4 and method 200disclose that the first step is electrospinning of the first anodelayer, the method may alternatively start with a first separator layeror a first cathode layer and then continue stacking the other layers inthe described (or similar) order. The repeating stacked structure may bedescribed using a repeating unit, such as a group including an anodelayer, a cathode layer and two separator layers, with a separator layerseparating each anode and cathode layer. For example, the group may bedescribed as an anode-separator-cathode-separator (A-S-C-S) group or aC-S-A-S group, or a S-A-S-C group, etc. Any suitable number of stackedgroups may be produced using method 200. In at least one embodiment, anelectrospun battery may be produced including 1 to 50 groups, or anysub-range therein. For example, there may be 1 to 30, 2 to 20, 5 to 20,or 10 to 20 groups. For batteries having only a single anode andcathode, the second separator may be eliminated.

Accordingly, following step 210 of method 200, one complete stack ofanode-separator-cathode is formed. In conventional battery architecture,a metal current collector would be required to be placed on each side ofthe stack in order to collect the electrical current generated in thebattery. These current collectors add weight and thickness to thebattery and limit the direction of lithium ion diffusion to onedirection. The disclosed method 200 allows for the elimination ofseparate current collectors, thereby reducing the weight and thicknessof the battery and allowing the lithium ions to diffuse in any directionacross any electrode.

Once the desired number of anode, separator, and cathode layers havebeen electrospun into a stack, the stack may be packaged to form acompleted battery. The battery may be in the form of, for example, acoin cell, pouch, or prismatic type cell. The battery may be filled witha liquid electrolyte, which fills the small pores in each layerresulting from the electrospinning process. The liquid electrolyteactivates the cell, allowing lithium ion transfer between the electrodeswhen an external circuit is connected to the collector tabs, such asthose created using the masks of FIG. 2. The electrolyte may be anysuitable electrolyte, and may include a lithium salt (e.g., LiPF₆, LiBF₄or LiClO₄) and an organic solvent (e.g., ethylene carbonate (EC),dimethyl carbonate (DMC), diethyl carbonate (DEC), or mixtures thereof).

While the method 200 of FIG. 4 is described above as usingelectrospinning to form the anode, cathode, and separator layers insteps 202, 206, 208, 212, and 214, other spinning methods may be used toform these battery components. For example, the components could beformed using wet spinning, dry spinning, melt spinning, extrusionspinning, direct spinning, gel spinning, or drawing. In addition,non-spinning methods may be used to form the components, as long as theanode and cathode layers can be carbonized to form a conductive layer.Furthermore, while the method 200 is described as being a generallycontinuous process, wherein each layer is directly spun onto thepreceding layer, it may be possible to form the layers separately andlater combine or assemble them into a stack. For example, batches ofanode, cathode, and separator layers could be separately prepared usingspinning (e.g., electrospinning) or other techniques. The anode andcathode layers could then be carbonized and the layers could beassembled to form a stack. However, the continuous process describedwith respect to FIG. 4 may provide a battery having better cohesionbetween the layers, since during the preparation they form asubstantially unified or continuous stack, rather than adjacentindividual components.

In addition to forming an electrospun battery on a standard collector,such as a flat conductive panel as shown in FIGS. 1 and 3, the method200 may be used to form batteries on other surfaces, such as vehiclecomponents, in order to utilize empty or unused spaces (e.g., in avehicle) for extra battery capacity. For example, the collector may beany metal component within a vehicle, such as the interior side of abody panel, trunk surface, or other areas. Non-conductive vehiclecomponents may be coated with a conductive material, have a conductivematerial attached thereto, or otherwise made conductive. The vehiclecomponent may then be grounded and used as the collector (e.g.,collectors 18 and 96 in FIGS. 1 and 3). Masks, such as those describedwith respect to FIG. 2, may be created to conform to the size and shapeof the component that is to be used as the collector. Once the desirednumber of layers of anode, separator, and cathode has been spun onto thecomponent, a film or some other form of protective barrier could beapplied to enclose the battery and form a completed cell. Accordingly,the disclosed methods may be used to form a custom battery on a vehiclecomponent in order to increase the battery capacity of a hybrid, plug-inhybrid, or electric vehicle. In addition to vehicle components, thedisclosed electrospinning process may be used on any surface to form abattery thereon.

With reference to FIG. 5, an electrospun battery 300 prepared accordingto method 200 is shown. The battery 300, as shown, includes fourseparator layers 310, two cathode layers 320, and two anode layers 330.A separator layer 310 contacts and separates each cathode layer 320 andanode layer 330. The separator layers are non-conductive and may beporous. No separate metal current collectors are present in the battery300 between groups of anode-separator-cathode layers. Instead, eachcathode layer 320 and anode layer 330 may be carbonized such that itincludes an electrically conductive bulk fiber. Each cathode layer 320may include a body 322 and a collector tab 324 and each anode layer 330may include a body 332 and a collector tab 334. The bodies 322 and 332may form the electrode field and the collector tabs 324 and 334 mayextend from the body portion and allow for connection to an externalcircuit. The collector tabs 324 and 334 may be formed at the same timeand using the same process as the bodies 322 and 332. Accordingly, thetabs 324 and 334 may also be formed of electrically conductive bulkfiber and may include the active materials. In at least one embodiment,the collector tabs 324 may extend from the bodies 322 of the cathodelayers in a different location than the collector tabs 334 extend fromthe bodies 332 of the anode layers 330. For example, if the bodies 322and 332 are generally rectangular, the collector tabs 324 and 334 may bepositioned on opposite ends of one side of the bodies, as shown in FIG.5. While each cathode layer 320 and anode layer 330 is shown with asingle collector tab, each layer may include multiple collector tabs.

The separator layers 310 may include a body 312 that is sized andconfigured to contact and separate the bodies 322 and 332 of the cathodeand anode layers, respectively. The separator layers 310 may have thesame or larger dimensions as the cathode and anode layers. For example,if the separator, cathode, and anode layer bodies are all generallyrectangular, the separator layer bodies 312 may have the same height andwidth as the cathode layer or anode layer bodies 322, 332 or one or bothof the height and width of the separator layer bodies 312 may be largerthan the height or width of the cathode and anode bodies 322, 332. Thedimensions of the separator layer bodies 312 may therefore ensure thatthere is no contact (e.g., electrical contact) between the bodies of thecathode and anode layers. However, the collector tabs 324 and 334 of thecathode and anode layers may extend beyond the separator layer bodies312, allowing for connection to an external circuit.

The anode layers 330 and cathode layers 320 may have similar dimensionsas standard architecture LIBs. The anode layers 330 may each have athickness of 10 to 100 μm, or any sub-range therein, such as 10 to 75μm, 20 to 75 μm, or 30 to 50 μm. The cathode layers 320 may each have athickness of 10 to 100 μm, or any sub-range therein, such as 10 to 75μm, 20 to 50 μm, or 20 to 40 μm. In one embodiment, the cathode layers320 may be thinner than the anode layers 330. The anode and cathodelayers may have thicknesses beyond the disclosed ranges, depending onthe design requirements. Generally, as the electrode thicknessdecreases, the battery power increased and as the electrode thicknessincreases, the battery capacity increases.

The separator layers 310 may also have similar dimensions as standardarchitecture LIBs, e.g., about 16 to 20 μm. However, the electrospinningprocess may allow for the separator layers to be thinner thanconventional separators. Standard architecture LIBs are constructed byassembling the individual electrodes and separator(s) into a stack,which requires that each component have mechanical properties robustenough to be handled. As a result, separator layers in conventional LIBsmust be at least about 16 μm or so thick in order to avoid tearing orother damage during handling. Since the battery 300 may be assembled byelectrospinning successive layers onto one another, no handling ofindividual separator layers is required. In addition, conventionalseparator layers are generally stretched in-plane (i.e., perpendicularto their thickness) during their preparation. This stretching can causetheir mechanical properties to be anisotropic, with their strength inthe thickness direction being reduced. The electrospinning processgenerally results in isotropic separator layers, resulting in increasedstrength in the thickness direction for a given thickness, compared toanisotropic separators. Accordingly, in electrospun battery 300, theseparator layer thickness can be reduced to a size based primarily onits required insulating properties, rather than mechanical properties.In one embodiment, the separator layers 310 may each have a thickness of1 to 20 μm, or any sub-range therein. For example, the separator layersmay each have a thickness of 1 to 16 μm, 1 to 15 μm, 1 to 12 μm, 1 to 10μm, 1 to 8 μm, or 1 to 5 μm.

The electrodes of the electrospun battery 300 may have a higher porositythan in conventional LIBs, due to the highly porous structure created bythe electrospinning process. Conventional electrodes may have a porosityof about 30 to 40%. The electrodes of the battery 300 may have aporosity of at least 40%, for example, 40 to 80% or any sub-rangetherein, such as 45 to 75%, 50 to 75%, 50 to 70%, or 60 to 70%. Theincreased porosity of the electrodes may increase cell power due toenhanced lithium ion diffusion within the electrolyte and improvedutilization of the active material in the electrodes.

The battery 300 may be packed in any suitable manner to form a completedbattery cell. For example, the battery 300 may be packaged as a coin,pouch, or prismatic type cell. The battery 300 may be filled with anelectrolyte, which may include a lithium salt (e.g., LiPF₆) and anorganic solvent (e.g., ethylene carbonate (EC), dimethyl carbonate(DMC), diethyl carbonate (DEC), or mixtures thereof).

The electrospun battery 300 may provide substantial weight and costssavings compared to conventional LIBs having metallic currentcollectors. For example, the electrospun battery 300 may lower thebattery cell cost by as much as 10% or more and may reduce the weight ofthe cell by as much as 15% or more. In addition to cost and weightsavings, the specific energy and energy density of the electrospunbattery 300 may be improved compared to conventional LIBs. Furthermore,the open porous structure of the electrospun electrodes 320 and 330 andthe interconnected electrically conductive fibers may improve the cellpower of the electrospun battery 300. The incorporation of the activematerial (e.g., nanoparticles of S, Li₂S or Si) in the fibers may alsoimprove the utilization of the active material, thereby furtherimproving cell performance and/or lowering active material costs. Theelectrical resistance of the conductive fibers in the electrodes may behigher than the resistance of conventional metallic current collectors(e.g., copper or aluminum), however, the above benefits compensate forthe reduced conductivity. In addition, the increased resistance may notbe a significant factor for battery designs with short conductive paths.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention. Furthermore,while the methods of forming a battery and the batteries formedtherefrom have been described with respect to lithium-ion batteries, themethods and the battery architecture disclosed may also be used forother energy storage devices. For example, the methods and architecturemay be applicable to other rechargeable battery types and supercapacitors.

What is claimed is:
 1. A vehicle body panel comprising: a metal insidesurface; a lithium-ion battery directly attached to the inside surfaceand including: a first anode layer including a conductive bulk fiber andan anode active material; a first non-conductive, porous layercontacting the first anode layer; a first cathode layer including aconductive bulk fiber and a cathode active material contacting the firstnon-conductive, porous layer; and a second non-conductive, porous layercontacting the first cathode layer.
 2. The vehicle body panel of claim1, wherein at least a portion of the anode active material is embeddedin the conductive bulk fiber of the anode layer and at least a portionof the cathode active material is embedded in the conductive bulk fiberof the cathode layer.
 3. The vehicle body panel of claim 1, wherein eachof the first anode and cathode layers includes a body and a collectortab extending from the body, the collector tab including a conductivebulk fiber.
 4. The vehicle body panel of claim 1, wherein the conductivebulk fiber of the first anode and cathode layers is a carbonizedpolymer.
 5. The vehicle body panel of claim 1, wherein the first andsecond non-conductive, porous layers are first and second separatorlayers.
 6. The vehicle body panel of claim 2, wherein the anode activematerial includes silicon nanoparticles.
 7. The vehicle body panel ofclaim 2, wherein the cathode active material includes sulfur.
 8. Thevehicle body panel of claim 1, wherein the first anode layer and thefirst cathode layer have a porosity of 40% to 80% and the first andsecond non-conductive, porous layers each have a thickness of 1 to 12μm.
 9. The vehicle body panel of claim 1 further comprising: a secondanode layer including a conductive bulk fiber and an anode activematerial contacting the second non-conductive, porous layer; a thirdnon-conductive, porous layer contacting the second anode layer; and asecond cathode layer including a conductive bulk fiber and a cathodeactive material contacting the third non-conductive, porous layer.
 10. Avehicle body panel comprising: a metal inside surface; a lithium-ionbattery directly attached to the inside surface and including: aplurality of anode layers, each including a conductive bulk fiber and ananode active material; a plurality of cathode layers, each including aconductive bulk fiber and a cathode active material; and a plurality ofnon-conductive separator layers, each separating an anode layer from acathode layer.
 11. The battery of claim 10, wherein the anode activematerial includes silicon and at least a portion of the anode activematerial is embedded in the conductive bulk fiber of each anode layer.12. The battery of claim 10, wherein the cathode active materialincludes sulfur and at least a portion of the cathode active material isembedded in the conductive bulk fiber of each cathode layer.
 13. Thebattery of claim 10, wherein no metal current collectors are in contactwith the plurality of anode layers or the plurality of cathode layers.14. The battery of claim 10, wherein the plurality of anode layers andthe plurality of cathode layers have a porosity of 40% to 80% and theplurality of non-conductive separator layers each have a thickness of 1to 12 μm.
 15. A method of electrospinning a battery onto a vehiclecomponent, comprising: (a) spinning a first electrode layer using aninside metal surface of the vehicle component as a collector; (b)spinning a first separator layer onto the first electrode layer; (c)spinning a second electrode layer onto the first separator layer; and(d) spinning a second separator layer onto the second electrode layer.16. The method of claim 15, further comprising repeating steps (a), (b),(c), and (d) to form a plurality of first electrode layers and aplurality of second electrode layers, each of the first and secondelectrode layers separated by a separator layer.
 17. The method of claim15 further comprising the steps of carbonizing the first electrode layerprior to step (b) and carbonizing the second electrode layer prior tostep (d).
 18. The method of claim 17, wherein the carbonizing steps areperformed using a laser.
 19. The method of claim 16, further comprisinga step (e) including enclosing the spun layers in a film after thespinning steps.
 20. The method of claim 16, wherein step (a) includesspinning a polyacrylonitrile (PAN) fiber and an anode active materialand step (c) includes spinning a PAN fiber and a cathode activematerial, or vice versa.